A gas turbine engine generally includes a core having, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section. During operation, an engine airflow is provided to an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section to the turbine section. The flow of combustion gasses through the turbine section drives the compressor section and is then routed through the exhaust section, e.g., to atmosphere.
During operation, the gas turbine engine may encounter airflow distortion in the engine airflow path upstream of the compressor section, such as a circumferential or local flow disruption due to the angle of attack of the gas turbine engine, a cross wind, or any other inlet anomaly. Airflow distortion can be so uneven during operation as to put portions of the compressor section at or below proper stall pressure ratios. In many cases, sufficient stall margin should be maintained in the compressor section in order to prevent stall conditions from occurring during operation of the gas turbine engine.
One approach to maintaining a desired stall margin in a gas turbine engine is to close the variable guide vanes at the inlet to the compressor section, thereby reducing air flow and pressure in the compressor section below a pressure sufficient to cause stall conditions. However, closing the variable guide vanes can decrease the overall efficiency of the gas turbine engine.